In order to make a surroundPanner Plug-in selectable as panner (Post-fader) in Nuendo, this Plug-in should have as subCategories : kSpatial or kSpatialFx (in order to use it as insert too). For example:
DEF_CLASS2 (INLINE_UID_FROM_FUID(Steinberg::Vst::SPannerProcessor::cid),
PClassInfo::kManyInstances,
kVstAudioEffectClass,
stringPluginName,
Vst::kDistributable,
Vst::PlugType::kSpatial ,
FULL_VERSION_STR, // Plug-in version (to be changed)
kVstVersionString,
Steinberg::Vst::SPannerProcessor::createInstance)
Be sure that you overwrite the function “tresult PLUGIN_API setBusArrangements …” which allows you to get the current bus arrangements.